1. Technical Field
This invention relates to compositions and methods useful for production of lightweight concrete roof tiles and more particularly, concerns the use of latex in admixture capable to produce such roof tiles. The lightweight concrete roof tiles thus produced, meet the Uniform Building Code Standard (UBCS) No. 32-12 for lightweight concrete roof tiles and is useful as a replacement for wood shingles and shakes, asphalt shingles, asbestos cement roofing, slates, etc.
As used herein, the term "lightweight concrete roof tile(s)" means a concrete roof tile with a specific gravity of about 1.06 to 1.38. Thus, for a lightweight concrete roof tile of conventional dimensions with a volume of about 2.163 liters, it will weigh about 2.727 kg.
As used herein, the term "strength test" means the strength test conducted according to UBCS No. 32-12, .sctn.32.1206 test procedure. First, a total of ten representative samples are selected from the lightweight concrete roof tiles production. The samples are then conditioned at a temperature of 73.degree..+-.5.degree. F. and 50% relative humidity for a period of twenty-eight days. At the end of the conditioning period, the weight for each specimen is recorded.
Five samples conditioned as above are subjected to the strength test.
The sample is tested as shown in FIG. 1 with the load applied at a uniform rate not exceeding ten pounds per second until failure. The breaking load is recorded to the nearest pound. The test is repeated three times and the average breaking load is determined.
For the tiles of the present invention, the average breaking load shall not be less than 300 pounds for five consecutive test samples or 250 pounds for any individual sample for the tiles to have passed the strength test.
As used herein, the term "water absorption test" means the water absorption test conducted according to the UBCS No. 32-12, .sctn.32.1206(b) test procedure.
A minimum of five samples from the tile fractured in the strength test are tested for water absorption. The sum of the dry weight for five samples at room temperature are more than 12 pounds. A total of five or more samples of the ridge and other accessory tile not subjected to the strength test are also tested. Their aggregate dry weight at room temperature of these samples are to be more than five pounds.
Loose particles are removed by scrubbing with a fiber brush and clean water. Samples are dried in a well-ventilated oven for twenty-four hours at a temperature of 221.degree..+-.3.6.degree. F. After drying, the samples are cooled at room temperature for fifteen minutes after identifying and weighing to the nearest 0.01 gram. The samples are then immersed in filtered or distilled water for 48 hours in a temperature of 68.degree..+-.9.degree. F. One sample is removed, surfaces wiped dry and weighed immediately. The process is repeated for each sample.
If the sample absorbs less than 15% water of its dry weight then the sample passes the water absorption test.
2. Description of Background Art
Methods to produce concrete roof tiles are well known. U.S. Pat. No. 4,673,659 teaches a method comprising forming a mix of cement, sand and water, extruding the mix by the well-known roller and slipper method, cutting the extruded mix to provide sections of the required length and curing at elevated temperatures under conditions of high humidity.
Roof tiles of essentially flat or with convoluted constructions are made in this way. Typically, they have densities ranging from 2.1-2.2 g/cc. Typical U.S. interlocking roof tiles have dimensions of about 422 mm (length).times.333 mm (width).times.11.5 to 12.5 mm (thickness). Such tile usually weighs 4.2 to 5.0 kg/tile, with strengthening ribs, nibs and weatherchecks, which are provided on the undersides of the concrete interlocking roof tiles, add to the overall weight.
Conventional concrete roof tiles of the kind described above provide a satisfactory and highly durable roofing material and are extensively used for the roofing of new houses and other buildings with sufficient supports. However, for re-roofing applications, a frequent problem is that the roofing material to be replaced may be of a lighter weight, such as for example wood shingles and shakes, asphalt shingles, asbestos cement roofing, slates, etc., thereby the building structure concerned may not be able to support the additional load structure resulted from re-roofing with conventional concrete roof tiles. For example, with timber framed buildings, it is often necessary to reinforce the existing roof timbers to ensure that they will bear the additional load. This is costly and time consuming which in practice often leads to abandoning the use of concrete roof tiles for re-roofing work.
Thus, there is continuous need for concrete roof tiles which are lighter in weight than conventional concrete roof tiles but have the adequate strength and durability of conventional concrete roof tiles. Such strong, durable lightweight concrete roof tiles will be useful as a suitable replacement for wood shingles and shakes, asphalt shingles, asbestos cement roofings, slates, etc.
Prior roof tiles and methods of production are disclosed, for example, in Jakel U.S. Pat. No. 3,841,885, Jakel U.S. Pat. No. 3,870,777, Kirkhuff U.S. Pat. No. 3,852,934, Murdock U.S. Pat. No. 4,288,959 and Wood U.S. Pat. No. 4,673,659.